Preparation and thermal properties of porous heterogeneous composite phase change materials based on molten salts/expanded graphite

• Molten salts/expanded graphite composite phase change materials were prepared.
• The content of molten salts in the composites was from 77.8% to 81.5%.
• Thermal conductivity of molten salts was enhanced after impregnation with EG.
• Composites showed great thermal stability after 40 cycles.
• Composites were designed for future use in cascaded latent heat storage.

Three kinds of porous heterogeneous composite phase change materials were synthesized from expanded graphite (EG) and binary molten salts (LiNO3–KCl, LiNO3–NaNO3 and LiNO3–NaCl) through solution impregnation method. Binary molten salt content in the composite phase change materials was calculated to be between 77.8% and 81.5% and high encapsulation efficiency was calculated to be between 72.8% and 78.8%. The thermal conductivity of binary molten salts was enhanced by 4.9–6.9 times after impregnation with EG. SEM photographs showed that the prepared composites were more homogeneous in comparison to other salt/EG composites prepared by infiltration or compression. Phase change properties of the porous heterogeneous composite phase change materials showed great thermal stability, which was maintained after 100 cycles.